冲积河流的河相关系

根据河流床沙的运动情况,将天然河流区分为三种类型,并分析其沿程河相关系。

CHANNEL GEOMETRY OF ALLUVIAL STREAMS

At present the study of channel geometry of alluvial streams is almost restrieted with empirical method in the realm of plain trar.t which ma nly carries suspended load.In this paper, according to the field data, using the ratio of threshold velocity and bankful velocity as index (Fig.1), the alluvial streams can be divieded into two main categories with different sizes of bed material, one is the river reach of gravel bed which is under the condition of threshold of motion, the other is the reach with sand bed which is with a live bed. The latter can be further divided into two sub-kinds, one is the reach of cobble bed which mainly carries bed load and the other is the reach of sand bed which mainly carries suspended load. There are two schools in the design of canals, tractive-force theory and regime theory, which are not two opposite ones but are the summary of two different kinds of motion of bed material t It is consistent with those of natural streams. The same law governs the motion of bed material of natural streams and canals.The downstream relations of hydraulic geometry of the said three types of river reaches are analysed with unified method in this paper. At the present time there are two approaches in the study of hydraulic geometry of rivers,one is the empirical approach propoed by Leopold et al.,and the other is a theoretical one. The latter is a method by solving simultaneous equations of the relations of the hydraulic and sediment variables. In this paper the two approa ches are combined together, using the equable distribution of variance among width, depth, velocity and stream power per unit bed area as a supplementary equation, and the equations for the downstream hydraulic geometry of alluvial rivers of the three types are obtained.For the threshold condition, equations (16) to (10) are of downstream hydraulic geometry, which are similar to the results of Li et al.For the bed load condition, equations are (24) to (27) are of downstream hydraulic geometry by using Dou's bed load formula; equations (29) to (32) are slightly different if other bed load formula is used such as Engelund-Hansen formula used in this paper.For the suspended load condition, equations are (37) to (40) are of downstream hydraulic geometry, which are similar to the results of Dou[11] and Langbein[12].Comparing the results of this paper with the field data, and other authors'results which are shown in figure 2 and table 4, the agreement is satisfactory.